Wavelength tunable properties of the perpendicular dual-grating guided-mode resonance filters

Perpendicular dual-grating (PDG) guided-mode resonance filters were constructed by placing two identical one-dimensional waveguide gratings close to and their grooves perpendicular to each other with a nano air gap between them. Multilayer waveguide theory was used to estimate the split of the resonant reflection peaks corresponding to the TE and TM modes, and the rigorous coupled wave analysis (RCWA) was used to investigate the resonant wavelength, the linewidth of the resonant peaks, and electric field intensity distribution in the filter structures. The filters present identical spectral characteristics for normally incident wave with arbitrary polarization. The TM01 and the TE01 modes are found displaying the greatest wavelength shift for the air gap variation between 0 and 100 nm, and 100 nm and 1000 nm, respectively. The coupling between the TE and TM modes is much greater in the g/w/a/w/g structure than that in the w/g/a/g/w structure, since there is no space between the two waveguide layers in the former. The resonant peaks of the TE01 mode for the one-dimensional PDG g/w/a/w/g structure exhibit narrower width compared with those for the two-dimensional g/w/a/w/g structure. In addtion, the horizontal shift between the two gratings does not influence the measured spectra, although it will certainly have great effect on the resonant peak width if the measurement were carried out by the guided-mode filters where the two gratings are two dimensional.